Field of the Invention
The present disclosure relates to a lithography apparatus, a pattern forming method, and a method for manufacturing a product.
Description of the Related Art
Lithography apparatuses for forming a pattern on a substrate are used to manufacture semiconductor devices and flat panel displays. Examples of the lithography apparatuses include an exposure apparatus and an imprint apparatus. High productivity and miniaturization technique are demanded of lithography apparatuses. A stage which is driven with a substrate or an original mounted thereon accordingly needs to be driven at a high speed and with high accuracy. For high-speed and high-accuracy stage control, the position of the stage is measured by using a high-resolution laser interferometer and a reflecting mirror that serves as a target of the laser light and has a flatness of high accuracy. As the driving range of the stage increases, the reflecting mirror increases in length. This has caused issues such as a difficulty in achieving a flatness of high accuracy and an increase in cost.
As an approach to address such issues, Japanese Patent Application Laid-Open No. 2002-319541 discusses a technique for performing position measurement by switching a plurality of laser interferometers. According to Japanese Patent Application Laid-Open No. 2002-319541, a plurality of laser interferometers is used and switched in an area where the plurality of laser interferometers can simultaneously make a measurement. In such a manner, position measurement and position control across the entire driving range of the stage are achieved.
A lithography apparatus performs a focus measurement process in a Z direction to obtain a focus offset before performing a process on a substrate. The lithography apparatus also performs an alignment measurement process in X and Y directions to obtain alignment offsets. The lithography apparatus then reflects the obtained focus and alignment offsets on stage control and performs the process on the substrate. If the focus measurement process in the Z direction is performed by using a plurality of laser interferometers, a position to switch the laser interferometers is determined in a coordinate system of stage driving. With the alignment offsets reflected on the stage control, the same processing target (for example, shot) may thus be measured by using different laser interferometers in the focus measurement process and in the process on the substrate.
In a case where the same process is performed on the same substrate for a plurality of times, the same processing target may be measured by using different laser interferometers. For example, if the alignment measurement process is performed for a plurality of times, the stage may be driven in different directions in the plurality of processes depending on the position of the stage when the previous process ends. Thus, even the same processing target (for example, alignment mark) may thus be measured by using different laser interferometers.
Further, in a case where the same process is performed on different substrates having the same shot layout, corresponding processing targets at the same positions on the substrates may be measured by using different laser interferometers. For example, in a case where the alignment measurement process is performed on corresponding alignment marks, the alignment marks on the different substrates may be measured by using different laser interferometers depending on a difference in the amount of positional deviation between each substrate and the substrate stage and a difference in the driving direction of the substrate stage.
Laser interferometers and reflecting mirrors have unique characteristics due to manufacturing errors. Depending on the unique characteristics, the same target measured by different interferometers may produce errors in the measurement result. Such measurement errors change the characteristic of the stage control.
Consequently, if a plurality of processes is performed on the same processing target or corresponding processing targets, the use of different laser interferometers for the stage control may cause a change in the characteristic of the stage control to decrease the accuracy of the stage control.